The conversion of PrPc to PrPsc is critical step in the pathogenesis and probably in the replication of transmissible spongiform encephalopathies. The mechanism by which this conversion occurs is not yet known but is hypothesized to involve the formation of a nucleus of PrPsc followed by growth of the polymer. The nucleation event is rate-determining and, in the case of human spongiform encephalopathies may take decades to form. Identification of factors, other than PrPsc, that are involved in this conversion may facilitate means of intervening in this process either by slowing the conversion process or by inhibiting the formation of the initial abnormal molecule. An experimental model system utilizing the denaturation and renaturation of PrPsc has been developed to examine compounds that affect PrPsc renaturation and infectivity as well as identify secondary molecules required for successful renaturation. Specifically, this model system will be used to address the following question: 1. What parameters produce consistent denaturation and renaturation of PrPsc? 2. Do compounds with amyloidogenic or anti-scrapie properties affect renaturation of PrPscand infectivity of the renatured samples? 3. Can denatured PrPsc-enriched preparations be fractionated into their component parts and then manipulated experimentally back to proteinase K- resistant and infectious material? The proposed experiments utilizing the denaturation/renaturation of PrPsc- enriched preparations will provide information about secondary molecules that influence the interaction of PrPsc with itself and with PrPc. The ability to equate PK-resistance of PrPsc with infectivity of the renatured samples will permit us to correlate in vitro events with in vivo events and may facilitate means of intervening in the disease process by either slowing the conversion process or inhibiting the formation/accumulation of the abnormal isoform of the protein.